In general, a large-sized transporter vehicle called a dump truck has a liftable vessel (loading platform) on a frame of a vehicle body, and transports crushed stones or the like in a state of the heavy baggage such as crushed stones being loaded in a large quantity on the vessel.
Therefore, each travel drive device for driving drive wheels of the dump truck for traveling is provided with an axle housing mounted in a non-rotating state on a vehicle body and having a tip end side opened to form a cylindrical spindle, a rotational shaft provided to axially extend in the spindle of the axle housing and driven and rotated by a drive source, a wheel mounting cylinder which is rotatably mounted on an outer peripheral side of the spindle through wheel support bearings and to which vehicle wheels are mounted, a reduction gear mechanism provided between the wheel mounting cylinder and the spindle to decelerate rotation of the rotational shaft, which is transmitted to the wheel mounting cylinder, and lubricant oil accommodated in a bottom side of the wheel mounting cylinder in a state of being reserved therein to lubricate the reduction gear mechanism (Patent Documents 1 and 2).
The reduction gear mechanism is constituted by a multi-stage planetary gear reduction mechanism comprising a sun gear arranged on an outer peripheral side of the rotational shaft and rotating with rotation of the rotational shaft, a plurality of planetary gears meshing with the sun gear and a ring-shaped internal gear, and a carrier rotatably supporting the respective planetary gears through support pins. The carrier forming apart of a final-stage planetary gear reduction mechanism is configured to be mounted in a non-rotating state on an open end side of the spindle.